A lithium-ion secondary battery is composed of a negative polar plate, a positive polar plate, an electrolytic solution and a membrane between the positive and negative polar plates for preventing a short circuit. The positive polar plate and the negative polar plate are formed as a thin plate or a foil. The electrical polar plates and the membrane therebetween are orderly stacked or helically wound so as to form a core, which is in turn embedded into a battery container made of a stainless steel, a nickel plated iron, an aluminum metal or a stacked flexible package thin film. Then, after electrolytic solution is injected into the battery container, the battery container is sealed and the battery is formed. The core is electrically connected to external components by a connection between tabs connected to the polar plates and a pole or a cover plate.
In the prior art, it is general that the tabs are welded at the pole of the cover plate. When a heavy current is discharged, for example, in a hybrid electrical vehicle (HEV) or an electrical vehicle (EV), if a connection at places such as the tabs and the pole is broken or inactive, a serious heating may occur, resulting in an overheating, even a failure, of the battery. Thus, the safety and cycle life of the battery may be influenced. In addition, the welding position may not be controlled accurately when a plurality of tabs are connected to the pole, which is unfavorable for the control of technology and quality.